Results from analysis of his genetic material appear in leading scientific journal Nature. They showed that he is the earliest known northern European.

Study leader Professor Carles Lalueza-Fox, from the Institute of Evolutionary Biology in Barcelona, said: "The biggest surprise was to discover that this individual possessed African versions in the genes that determine the light pigmentation of the current Europeans, which indicates that he had dark skin, although we cannot know the exact shade.

"Even more surprising was to find that he possessed the genetic variations that produce blue eyes in current Europeans."

La Brana 1 had a "unique phenotype" - or set of characteristics - in a genome that was otherwise "clearly northern European", he said.

His was one of two unusually well preserved male skeletons unearthed from the La Brana-Arintero cave system near Leon in 2006.

The scientists focused first on La Brana 1's DNA because it was in better condition. They hope in due course to piece together the genome of the other man, La Brana 2.

Both individuals have been dated to around 7,000 years old. They lived in the Mesolithic period, which ended 5,000 years ago with the development of agriculture and livestock farming in the Middle East.

He also shared a common ancestor with people who inhabited the Upper Palaeolithic site of Mal'ta, near Lake Baikal, Siberia, more than 20,000 years ago.

DNA from one of the Siberians, a boy, last year revealed links with native Americans.

"These data indicate that there is genetic continuity in the populations of central and western Eurasia," said Prof Lalueza-Fox.

La Brana 1's genome hints at some of the changes that occurred in humans as a result of switching from a hunter-gatherer existence to farming.

He would have been unable to digest lactose in milk or to cope with the starchy food that became the mainstay of later Neolithic farmers.

Farming is thought to have driven changes in the human immune system as a result of exposure to bacteria and viruses from animals.

But a number of DNA variants conferring resistance to infection in modern Europeans were already present in the hunter-gatherer.

This suggests they did not arise as an adaptation to farming, but had a more ancient origin.

The mixture of African and European traits implies that long after modern humans left Africa their racial transformation was still in progress, with changes in eye colour coming before alterations in skin tone.

Writing in Nature, the scientists concluded: "Our results indicate that the adaptive spread of light skin pigmentation alleles (genetic variants) was not complete in some European populations by the Mesolithic, and that the spread of alleles associated with light/blue eye colour may have preceded changes in skin pigmentation."